Milk production has a significant impact on the nutrient requirements of cattle. Understanding differences in milk production due to age or genetics, the milk production curve and how milk production affects requirements for energy is important for hay feeding and supplementation strategies.
For beef cows, the pounds of milk produced per day by a cow increase from calving until about 60 days after calving, at which time it peaks. From peak milk production until weaning, daily milk production decreases until calves are weaned. Table 1 provides estimates of daily milk production (pounds per day) and energy requirements (megacalories per day) for milk production for a mature beef cow that has the genetic potential to peak at 20 pounds of milk.
Age also affects milk production. For example, if the genetic potential for milk production and diet are the same, 2-year-old cows generally produce less milk than 3-year-old cows. Additionally, 3-year-old cows generally produce less milk than cows that are 4 to 10 years old. After cows reach about 10 years old, milk production starts to decline again.
On most cow-calf operations, there are multiple cuttings or lots of hay available for feeding each winter. These cuttings or lots will vary in quality, and selecting one cutting over another to feed at a certain time can have significant impacts on cow body condition score, pregnancy rates and supplementation cost.
Generally, it is best to feed hay with the highest level of TDN (total digestible nutrients, a measure of the energy content of a feed) during the first 90 days after calving. This reduces the amount of supplementation needed and helps cows come back into heat sooner after calving.
Lower-quality hay should generally be fed to non-lactating cows or saved and fed to lactating cows that have lower nutrient requirements (i.e., those cows 120 days or more post-calving). If cool-season annual forages will be available for limit grazing, consider saving lower-quality hay to be fed at this time. Limit grazing is cheaper than feeding higher amounts of concentrate supplements.
